Many fractures of long bones can be satisfactorily stabilized by the surgical insertion of a shaft, rod or nail into the intramedullary canal of the bone. Since the natural canal is irregular in internal diameter and configuration from end to end, and since all intramedullary fixation devices gain strength with increases in diameter, most surgical procedures call for incremental reaming with sequentially used reamers having 0.5 mm or 1.0 mm inmcreases in outside diameter. Because the shafts of most long bones are bent or curved along their longitudinal axes, flexible shafts that can bend to follow this naturally curved path while transmitting torque are necessary in the art of intramedullary reaming so as to prevent the reamer from cutting through the wall or cortex of the bone. If the reamer shaft is inflexible and thereby does not follow the natural curvature of the bone, the reamer head may in fact cut through the wall or cortex of the bone being reamed.
Presently marketed flexible intramedullary reamer shafts are designed in such manner that they store rotational energy in a spring manner whenever the cutting head stops or gets caught by the bone structure. When this happens, the driving motor continues to turn the proximal end of the shaft to thereby increase the torque and to thereby store energy in the shaft until the force exerted by the shaft exceeds the force which is retaining the cutter head. At this point, the cutter head becomes dislodged thereby allowing the release of the stored rotational energy so that the cutter head springs, jumps, or spins ahead rapidly in an uncontrollable fashion within the bone. In many cases, the above described scenerio repeats itself over and over again to thereby cause what is known in the art as "chatter". These irregular, uncontrollable movements of the reamer head caused by the spring-like shaft may damage the bone and act to greatly increase the risks of surgical complications. Two examples of prior art constructions exhibiting the above described characteristics are illustrated herein in FIGS. 1 and 2 respectively, and will be described in greater detail hereinafter.
One particular problem occurs frequently in the prior art shaft shown in FIG. 1. This shaft may only be used in a forward rotational direction since if it is inadvertently or intentionally used in reverse, the spring-like shaft may unwind and virtually self-destruct. This often occurs when a surgeon attempts to reverse the rotational motion of the cutter head to dislodge it. In a further problem typical of prior art reamer shafts which are made of multiple strands of wire, cable, or strap material wrapped in a helical fashion, blood may enter the spaces between the various associated parts thereof, which blood or tissue may not be readily removed and could in fact become a danger to subsequent patients.